In the semiconductor packaging industry, semiconductor chips are typically attached to substrates such as leadframes or BGA substrates during the fabrication process. After electrical connections are made between these semiconductor chips and the substrates, the semiconductor chips are encapsulated with encapsulation material (such as resin) using molding processes. After molding, the substrates are processed to remove cull formed during molding, and the encapsulated semiconductor chips are then singulated to complete the packaging process.
During the packaging process, and in particular during molding, the substrate is heated prior to and during the molding process. The increased temperature is required to allow the encapsulation material to form properly on the substrate and around the semiconductor chip. After the molding process is completed, the substrate is cooled before the cull is removed. Due to the heating and cooling of the substrate during the aforementioned process, the substrate is subjected to thermal expansion and contraction. As a result, warpage would tend to occur in the substrate, which affects the quality of the final product. Furthermore, warpage may cause damage to the fragile semiconductor chip.
Various methods have been devised to reduce warpage caused by such thermal expansion and contraction. Many of these methods utilize material formulation methods, to manufacture the substrate with certain physical properties to make it less prone to warpage.
Another method may be to include a metal layer surrounding the substrate areas to increase the stiffness of the entirety of the strip of substrate, such as in U.S. Pat. No. 6,369,439 for “Strip of Semiconductor Package”. Nevertheless, using special material formulations or adding layers of support to the substrates involve increased manufacturing costs, and they may not reduce warpage sufficiently to justify the increased costs.
Therefore, it would be advantageous to adopt an apparatus and method to reduce warpage to substrates during a semiconductor packaging process without having to resort to special formulations or constructions of the substrates.